THE UTILITY OF BODY-MASS INDEX AS A MEASURE OF BODY FATNESS IN CHILDREN AND ADOLESCENTS - DIFFERENCES BY RACE AND GENDER

Objective. To evaluate whether body mass index (BMI) is a representati ve equivalent measure of body fatness independent of age, race, gender , sexual maturation, and distribution of fat in children and adolescen ts. Study Design. Cross-sectional study of 192 healthy subjects (100 b oys and 92 girls, 103 white and 89 black) age 7 to 17 years. Methods. Height and weight were measured in the standard fashion, and BMI (kg/m (2)) was calculated from these values. Fat mass and percent body fat w ere determined using dual-energy x-ray absorptiometry. Sexual maturati on was evaluated by physical assessment. Distribution of fat was deter mined by the waist:hip ratio. Results. There were no significant diffe rences by gender and ethnic group for any of the demographic or anthro pometric variables, except waist:hip ratio, which was higher in white compared with black boys. BMI was significantly and positively correla ted with age, stage of maturation, and all of the anthropometric varia bles in each race-sex group. The correlation of maturation stage with BMI was stronger than the correlation between age and BMI. A multiple regression analysis showed that BMI, gender, race, sexual maturation, and distribution of fat were all significant independent correlates of the percent body fat (multiple R-2 = .77). The percent body fat-BMI r elationship was dependent on the stage of sexual maturation, gender (f or an equivalent BMI, girls have greater amounts of body fat than boys ), race (for equivalent BMI, whites have higher body fat than blacks), and waist:hip ratio (for equivalent BMI, those with central obesity h ave greater body fatness than those with peripheral obesity). Conclusi on. BMI is not an equivalent measure of the percent body fat for each race-sex group. When BMI is used as a measure of body fatness in a res earch or clinical setting, particularly when comparisons are made acro ss race and gender, it may be important to consider the maturation sta ge, race, gender, and distribution of body fat in the interpretation o f the results.